This invention is related to varactor television tuning systems which vary tuning frequency by a change in the application of voltage to a varactor diode tuning device. More specifically, it relates to the form of varactor television tuning systems which selectively tune to desired television channels according to a predetermined channel program sequence which has been stored in a memory.
A versatile memory tuning system is completely disclosed and claimed in application Ser. No. 466,579, filed May 3, 1974, now U.S. Pat. No. 3,946,319 issued Mar. 23, 1976, in the names of John Ma and Akio Tanaka and entitled "All Electronic Digital Tuner System with Memory" and assigned to the assignee of the present application. The memory may be programmed in any desired sequence to provide sequential tuning among a selected group of channels. The advantages of such a tuning system with a memory are readily apparent since the viewer need sequence through only desired channels. The memory has sufficient capacity to hold the digits of the desired channel number, normally in binary encoded decimal form. The speed at which memory locations are accessed and the stored tuning information extracted is so rapid that the change of stored selections appears to be instantaneous. This rapid access speed is an important feature of memory systems.
A characteristic of all memory tuning systems is that they normally have two modes of operation, a program mode in which channel selections are made and an operate mode in which channel selections are recalled. With varactor diode tuners, channel selection involves supplying a proper DC tuning voltage to the tuner. The mechanism for supplying the proper voltages may range from digitally accessed adjustable potentiometers to binary memories for storing channel numbers. In the operate mode the viewer then only sweeps through the limited number of preselected channel numbers for tuning to the desired channel.
Application Ser. No. 457,010, now U.S. Pat. No. 3,931,579 issued Jan. 16, 1975, filed Apr. 1, 1974, in the name of Akio Tanaka entitled "Digital Signal Seeking Tuning System" and assigned to the assignee of the present application discloses a television tuning system which includes channel counters operating sequentially to generate desired channel numbers. As each channel number is generated the system responds by tuning to the frequency location corresponding to the channel number. The system also utilizes signal recognition means to determine if a receivable signal is present at that frequency location and stops additional channel number generation until reactivated by the viewer. This use of channel counters to generate channel number information greatly simplifies the tuning system for the viewer but no provision is made for a memory to store selected information.
A memory of the type which could store individual binary encoded channel number digits could be added to such a system to provide for a convenient method of selecting from all possible channels only those channels which the viewer desires. Such a memory is described in the related application. As with all memory systems, in the program mode the operator wishes to select among all available channels and create the sequence of desired channels available in his locations for subsequent viewing. In the operate mode the viewer will then choose from those selected channels the particular channel he wishes to view. To maintain an important feature of memory systems, the recall of information for tuning must be extremely fast. But with this system a single device, the counter, both generates tuning information and accesses memory locations to determine if it has been selected. A problem arises with a single speed system since making selections in the program mode will be very difficult because of the rapid speed required for recall or in the alternative making selections in the operate mode would become annoyingly slow since the speed of operation would have to be slow enough to allow for proper selections in the program mode.
The present invention relates memory tuning systems employing counters and apparatus for controlling the speed at which the counters advance to generate channel number information to produce different speeds in the program and operate modes. Thus, the viewer can make comfortable selections during the program mode and still have the very rapid access through the selected channel numbers in the operate mode.